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tmi-practicum-2018-2019/TMI-practicum/SweepLineEffAlgorithm.cs
2019-05-19 13:23:10 +02:00

174 lines
6.2 KiB
C#

using System;
using System.Collections.Generic;
using Medallion.Collections;
namespace TMI_practicum
{
public static class SweepLineEffAlgorithm
{
public static IEnumerable<Intersection> Solve(IEnumerable<Circle> circles)
{
var intersections = new HashSet<Intersection>();
var events = new PriorityQueue<Event>();
var active = new C5.TreeDictionary<SegmentKey, Circle>();
foreach (var circle in circles)
{
events.Enqueue(new Event(Event.EventType.Start, circle.X - circle.R, circle, circle.Y));
events.Enqueue(new Event(Event.EventType.End, circle.X + circle.R, circle, circle.Y));
}
while (events.Count != 0)
{
Event e = events.Dequeue();
int hash = e.GetHashCode();
switch (e.Type)
{
case Event.EventType.Start:
active.Add(
new SegmentKey(e.Circle.X, e.Circle.Y + e.Circle.R, SegmentKey.SegmentType.Upper, hash), e.Circle);
active.Add(
new SegmentKey(e.Circle.X, e.Circle.Y - e.Circle.R, SegmentKey.SegmentType.Bottom, hash),
e.Circle);
CheckIntersections(active, e, intersections, true, events);
CheckIntersections(active, e, intersections, false, events);
break;
case Event.EventType.End:
CheckIntersections(active, e, intersections, true, events);
CheckIntersections(active, e, intersections, false, events);
active.Remove(new SegmentKey(e.Circle.X, e.Circle.Y + e.Circle.R, SegmentKey.SegmentType.Upper,
hash));
active.Remove(new SegmentKey(e.Circle.X, e.Circle.Y - e.Circle.R, SegmentKey.SegmentType.Bottom,
hash));
break;
case Event.EventType.Intersection:
CheckIntersections(active, e, intersections, true, events);
CheckIntersections(active, e, intersections, false, events);
break;
default:
throw new ArgumentOutOfRangeException();
}
}
return intersections;
}
private static void CheckIntersections(C5.TreeDictionary<SegmentKey, Circle> active, Event e,
HashSet<Intersection> intersections, bool upper, PriorityQueue<Event> events)
{
C5.KeyValuePair<SegmentKey, Circle> other;
if (upper)
{
if (!active.TrySuccessor(new SegmentKey(e.X, e.Y, SegmentKey.SegmentType.Upper,
e.GetHashCode()), out other))
return;
}
else
{
if (!active.TryPredecessor(
new SegmentKey(e.X, e.Y, SegmentKey.SegmentType.Bottom, e.GetHashCode()), out other))
{
return;
}
}
var intersects = e.Circle.FindIntersections(other.Value);
if (intersects == null) return;
foreach (var intersection in intersects)
{
if (intersections.Contains(intersection)) continue;
events.Add(new Event(Event.EventType.Intersection, intersection.X, e.Circle, intersection.Y));
intersections.Add(intersection);
}
}
private struct Event : IComparable<Event>
{
public EventType Type { get; }
public Circle Circle { get; }
public double X { get; }
public double Y { get; }
public enum EventType
{
Start,
Intersection,
End
}
public Event(EventType type, double x, Circle circle, double y)
{
Type = type;
X = x;
Circle = circle;
Y = y;
}
public int CompareTo(Event other)
{
return X.CompareTo(other.X);
}
public override int GetHashCode()
{
unchecked // Overflow is fine, just wrap
{
int hash = 17;
// Suitable nullity checks etc, of course :)
hash = hash * 23 + Type.GetHashCode();
hash = hash * 23 + X.GetHashCode();
hash = hash * 23 + Y.GetHashCode();
return hash;
}
}
}
private struct SegmentKey : IComparable<SegmentKey>
{
private readonly double _x;
private readonly double? _y;
private double Y => _y ?? double.MinValue;
private readonly SegmentType _type;
private readonly int _identifier;
public SegmentKey(double x, double y, SegmentType type, int identifier)
{
_y = y;
_type = type;
_identifier = identifier;
_x = x;
}
public int CompareTo(SegmentKey other)
{
if (_identifier.Equals(other._identifier)) return _type.CompareTo(other._type);
if (!_y.Equals(other._y)) return Y.CompareTo(other.Y);
return _type.Equals(other._type) ? _x.CompareTo(other._x) : _type.CompareTo(other._type);
}
public override bool Equals(object obj)
{
if (obj == null || GetType() != obj.GetType()) return false;
SegmentKey r = (SegmentKey) obj;
return _identifier.Equals(r._identifier) && _type.Equals(r._type);
}
public override int GetHashCode()
{
return _identifier.GetHashCode() ^ _type.GetHashCode();
}
public enum SegmentType
{
Bottom,
Upper
}
}
}
}